Significant promotional effect of CCl4 on fullerene yield in the graphite arc-discharge reaction

Article abstract of DOI:10.1039/b306921b

Addition of a small quantity (～3%) of CCl₄ to the He atmosphere of the graphite arc-discharge reaction revealed a marked increase in fullerene yield.

Full text of DOI:10.1039/b306921b

Significant promotional effect of CCl4 on fullerene yield in the graphite
arc-discharge reaction†
Fei Gao, Su-Yuan Xie,* Rong-Bin Huang and Lan-Sun Zheng
State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemistry, Xiamen
University, Xiamen, 361005, P. R. China. E-mail: syxie@jingxian.xmu.edu.cn
Received (in Corvallis, OR, USA) 16th June 2003, Accepted 4th September 2003
First published as an Advance Article on the web 24th September 2003
Addition of a small quantity ( ~ 3%) of CCl4 to the He
atmosphere of the graphite arc-discharge reaction revealed a
marked increase in fullerene yield.
mixed into He atmosphere remarkably enhances the fullerene
formation in the graphite arc-discharge reaction. This finding
will be of significance for large scale fullerene synthesis, and
provides valuable clues to the investigation of the mechanism of
fullerene formation.
Since macroscopic quantities of C60 and other fullerenes were
prepared by the method of graphite arc-discharge in a He
atmosphere by Krätschmer and Huffman in 1990,1 various
alternative methods have been reported to produce fullerenes.
These include incomplete combustion of benzene or hydro-
carbons2 (the combustion method has now been extended to
large scale fullerene production by the Mitsubishi Corpora-
tion),3 pyrolysis of naphthalene,4 and dissociation of hydro-
carbons in thermal plasma.5,6 However, arc-discharge between
graphite rods under a low-pressure of inert-gas remains one of
the most efficient processes.
In the past decade, great efforts have been focused on
optimizing reaction conditions in graphite arc-discharge for
fullerene preparation. Variations include the type and pressure
of foreign gases,7,8 the shape and composition of graphite
electrodes,9,10 and the reaction temperature.11,12 In previous
reports,13–15 fullerene C60 can be synthesized in relatively good
yield (e.g. up to 15% or more under optimal reaction
conditions). The cost of fullerenes by this method, however, is
still prohibitively expensive for industrial applications. There-
fore, simpler and more efficient methodology must be found to
reduce the cost. We now report that a small amount of CCl4
In the present experiment, graphite arc-discharge was
performed under an atmosphere of He, CCl4, or mixtures
thereof. The setup (see ESI)† includes a stainless steel cylinder
reactor (30 cm I.D. 3 50 cm) equipped with two graphite
electrodes: a block of graphite (cathode, with a diameter of 130
mm and a thickness of 15 mm) and a graphite rod (anode, 6 mm
in diameter and 15 cm in length). After discharge reaction at 24
V and 100 A for half an hour, about 3–4 g of soot was produced.
In each run, 2.7 g was collected for extraction with 150 ml
toluene in a Soxhlet extractor. To study the effects of the He/
CCl4 medium and pressure on fullerene production, the toluene-
soluble extract was condensed to 25 ml for examination of the
product by reverse phase liquid chromatography and ultraviolet
spectrometry (LC-UV) using a TSP Model P2000 HPLC
coupled with a TSP UV3000 detector. Analysis focused on the
relative yields of C60 and C70 versus consumed graphite
reactant, estimated from their peak areas in the HPLC-UV
chromatograms of the toluene-soluble products detected at 330
nm. A chromatographic example and the linear correlation plots
of peak areas against fullerene concentrations are shown in the
ESI† The fullerene yields (C60 and C70) under various reaction
conditions, and peak areas, as well as the amounts of consumed
graphite reactant and collected soot product, are listed in Table
1.
† Electronic supplementary information (ESI) available: diagram of the
experimental setup used; linear correlation plots of chromatographic peak
area vs. fullerene concentration (C60 and C70); typical HPLC-UV chromato-
gram of the products; data for four repeats of experiments 4 and 5. See http:
//www.rsc.org/suppdata/cc/b3/b306921b/
Among the many reports regarding fullerene synthesis by
graphite arc-discharge with different foreign gas additives (He,
Ar, N2, Cl2, C2N2 and CH3OH etc.), a He atmosphere has been
Table 1 Fullerene yields in different CCl4/He atmospheres
Chromatographic peak
areas (mA.U. 3 min)
Fullerene weights
in 2.7 g soot/mg
Fullerenes
yieldsa (%)
Experimental conditions
Consumed
graphite
reactant/g
Experi-
ment no.
Collected
soot/g
CCl4/Torr
He/Torr
C60
C70
C60
C70
C60
C70
1
2
3
4
5
6
7
8
9
10
11
12
13
0
0
0
0
40
80
300
300
300
300
0
0
40
70
170
210
3.53
3.24
2.90
2.80
1.45
1.79
1.88
1.93
1.50
0.82
1.11
1.30
1.59
3.40
3.13
2.89
2.78
2.70
3.33
3.76
4.00
3.44
2.74
2.80
2.94
3.15
< 4
< 4
< 4
465
1224
757
481
< 4
31
48
175
216
289
< 4
< 4
< 4
119
318
168
146
< 4
12
29
52
81
107
< 0.6
< 0.6
< 0.6
73.2
192.7
119.2
75.7
< 0.6
4.9
< 0.3
< 0.3
< 0.3
9.6
25.7
13.6
11.8
< 0.3
1.0
2.3
4.2
6.5
8.6
< 0.02
< 0.02
< 0.02
2.7
13.3
8.2
5.6
< 0.05
0.4
1.0
2.6
2.8
3.3
< 0.01
< 0.01
< 0.01
0.4
1.8
0.9
0.9
< 0.02
0.1
0.3
0.4
0
10
20
40
130
40
40
40
40
40
7.6
27.6
34.0
45.5
0.5
0.6
a The fullerene yields are calculated by dividing the grams of fullerenes (C60, C70) obtained by the grams of graphite consumed. It is difficult to calculate
the actual conversion of fullerenes from the total carbon sources (i.e. the carbon from both the graphite and the CCl4 consumed), because the grams of the
consumed CCl4 cannot be determined exactly in the present experiments. The carbon source from the CCl4, however, is deduced to be very little. As an
example, 1.45 g of graphite was consumed but 2.70 g of soot was produced in Experiment no. 5. The obtained soot was 1.25 g more than the consumed
graphite, and this extra mass was reasonably supposed to come from the CCl4. Among the 1.25 g consumed CCl4, only 0.097 g carbon might become the
source for fullerenes, this weight is much lighter than the consumed graphite (1.45 g). Therefore, the fullerene conversion from both the graphite and CCl4
consumed may be approximatively replaced by the fullerenes yield as listed here.
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This journal is © The Royal Society of Chemistry 2003

confirmed to be the best medium to promote fullerene
formation.7–15 In agreement with the previous investigations,
the fullerene yields in our reactor were optimized at a He
pressure of about 300 Torr; the yield rapidly decreased on either
increasing or decreasing the He pressure. It should be noted that
the setup employed for the present experiments was not the
most favorable one for fullerene production, and the yield of C60
and C70 from graphite arc-discharge in ambient He were
determined to be less than those previously reported.13–15 The
addition of CCl4, however, brings our inferior fullerene
generator up to the equal of the best previously reported C60
generators. As shown in the HPLC-UV chromatogram in the
ESI,† fullerenes as well as various chlorinated carbon clusters
(CCCs), such as C6Cl6, C10Cl8, C12Cl8, C14Cl8, C16Cl10 and
C60Cl8, were produced from the graphite arc-discharge reac-
tions in the presence of CCl4. The latter CCCs were similar to
those obtained in the studies of chloroform glow discharge16,17
and microwave plasma.6 The structures of some CCCs were
determined from their molecular formulae coupled with the
characteristic retention times of reference compounds identified
in previous studies.18 In the present studies they were not
determined quantitatively. As indicated in Table 1, spectacular
enhancements of fullerene yields were obtained when a small
partial pressure of CCl4 (10 Torr) was present (experiments 4
and 5). The repeatability in the proposed process was shown to
be reasonable (see table in ESI,† where data for four repeats of
experiments 4 and 5 are shown). Surprisingly, on sequentially
increasing the partial pressure of CCl4 to 20 and 40 Torr, the
fullerene yields declined rapidly (experiments 5–7), while the
total yield of CCCs increased concurrently. It was also revealing
that when the graphite arc-discharge was run in a pure
atmosphere of CCl4 at 130 Torr (experiment 8), only CCCs and
very little fullerenes were detected. It could be expected that
fullerenes might thoroughly dominate over the products and
CCC yields could be reduced to nearly zero when decreasing the
CCl4 partial pressure to a narrow value. This would remove the
need for the purification of fullerenes from the CCCs mixture
and prevent the fullerene generator from eroding in superfluous
chlorinated species.
mediates are stabilized in some way. Accordingly, we believe
that trapping the fullerene intermediates (i.e. the CCCs) in the
reaction and estimating the relationship between yields of CCCs
and fullerenes could be of significance for investigation of the
fullerene formation mechanism.
To test the cooperative effect of CCl4 and He, the former was
held at 40 Torr and the effect on the fullerene yield was studied
by varying the He partial pressure. As shown in experiments
9–13, the yields increased steadily as He partial pressure was
increased from 0 to 210 Torr. Together with experiment 7, these
demonstrated the cooperative effect of CCl4 and He on the
fullerene formation process.
In conclusion, while the yields of fullerenes from our inferior
reactor are only comparable to those obtained in the best
fullerene generator previously reported,12–14 the major finding
that the enhancement of fullerene formation via the addition of
CCl4 would not only be helpful for the mechanistic investiga-
tion of fullerenes but also amenable to practical preparation of
fullerenes. It could be expected that the addition of a small
quantity of CCl4 to the optimal fullerene generator might
significantly increase the best fullerene yields previously
reported13–15 to some extent.
This work was supported by the Natural Science Foundation
of China (Grant No. 20021002, 20273052 and 20001005), the
Ministry of Science and Technology of P.R.C.
(2002CCA01600) and the Ministry of Education of P.R.C.
(03096). The authors would like to thank Professor Yuan L.
Chow for valuable suggestions and generous help.
Notes and references
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ters in the arc-discharge have free valences. These reactive
intermediates have long lifetimes to grow to fullerenes (inert
media with hot carbon atoms). Addition of some foreign species
such as hydrogen or halogen, however, causes the free valences
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